- Chiral preparation of polyoxygenated cyclopentanoids
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A series of polyoxygenated cyclopentanoids, including 2,2-dimethyl- 3a,6a-dihydro-4H-cyclopenta[d][1,3]dioxol-4-one, has been prepared in both enantiomeric forms from cyclopentadiene by employing lipase-mediated kinetic resolution as the key step. Thus, cyclopentadiene is first transformed into racemic cis-4-cumyloxycyclopent-2-en-1-ol which is resolved under transesterification conditions in the presence of lipase PS. After transformation into the corresponding tert-butyldimethylsilyl (TBS) ethers, each of the enantiomers is cis-dihydroxylated diastereoselectively from the less hindered face which is transformed into the 2,3-O-isopropylidene-1,4-di- O-protected (trans-1,2:cis-2,3:trans-3,4)-1,2,3,4-cyclopentanetetraol. Selective removal of the 1,4-protecting group gives the corresponding 2,3,4- O-protected cyclopentanols which are further transformed into the 2,3,4-O- protected cyclopentanones on oxidation without suffering β-elimination. Exposure of the cyclopentanones to warm acetic acid allows β-elimination to give rise to the dehydration product 2,2,-dimethyl-3a,6a-dihydro-4H- cyclopenta[d][1,3]dioxol-4-one having the corresponding chirality without losing their original chiral integrity.
- Nakashima, Hiromi,Sato, Masayuki,Taniguchi, Takahiko,Ogasawara, Kunio
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p. 817 - 823
(2007/10/03)
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- Lipase-mediated resolution of cis-4-cumyloxy-2-cyclopenten-1-ol and its utilization for enantioconvergent preparation of (-)-oxabicyclo[3.3.0]oct-6- en-3-one
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Convenient preparation of both enantiomers of cis-4-cumyloxy-2- cyclopenten-1-ol from cyclopentadiene employing a lipase-mediated resolution was first established. An efficient enantioconvergent transformation of both enantiomeric products affording (-)-oxabicyclo[3.3.0]oct-6-en-3-one, an important building block of prostaglandin synthesis, was next established.
- Nakashima, Hiromi,Sato, Masayuki,Taniguchi, Takahiko,Ogasawara, Kunio
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p. 1754 - 1756
(2007/10/03)
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- Photochemical Cycloadditions. III. Addition of 4-Substituted 2-Cyclopentenones to Allene; Configuration Determination by Lanthanide-Induced Shift Studies
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Photoaddition of 4-substituted 2-cyclopentenones to 1,2-propadiene gave mixtures of the head-to-head and head-to-tail cycloadducts in a ratio of ca. 90:10.The stereoisomeric composition was sensitive to solvent changes, as was the chemical yield of the cycloadducts.Under otherwise identical conditions the highest yields were obtained in non-polar solvents.The configurations of the cycloadducts were determined by LIS and 13C NMR studies.
- Stensen, Wenche,Svendsen, John S.,Hofer, Otmar,Sydnes, Leiv K.
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p. 259 - 268
(2007/10/02)
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- STUDIES ON THE ASYMMETRIC TOTAL SYNTHESIS OF TRICHOTHECENES. STEREOSELECTIVE CONSTRUCTION OF THE C-RING FRAGMENT
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A stereoselective construction of the C-ring fragment of trichothecenes from readily available 4-cumyloxy-2-cyclopentenol in 12 steps (24percent overall yield) is described.
- Hua, Duy H.,Venkataraman, S.
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p. 3765 - 3768
(2007/10/02)
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